The present invention relates to an optical device for a color copy machine and the like which is capable of forming an object image on a light receiving plane at different magnifications.
Conventionally, this kind of optical device is constructed as follows:
A zoom lens is mounted on a carriage, and a carriage drive mechanism is disposed on the base plate on the side of the main body of the copy machine. Further, a guide rail for guiding the carriage is disposed in the direction of the optical axis of the zoom lens. Further, pulleys and a wire are interposed between the carriage and the carriage drive mechanism for transmitting the driving force of the drive mechanism to the carriage. Thus, the carriage is driven by the carriage drive mechanism by means of the pulleys and the wire, and is moved in the direction of the optical axis of the zoom lens as the carriage drive mechanism is operated.
In the construction described above, a stray light prevention member covering the zoom lens from the upper side thereof is provided for preventing stray light caused by an illuminating light from entering the zoom lens.
Nevertheless, in the conventional devices, since the carriage drive mechanism is mounted on the main body, an escape portion is interposed between the stray light prevention mechanism and the carriage drive mechanism so that they are not brought into contact to each other. Even if a small amount of a stray light enters the zoom lens through the slight gap of the escape portion, a formed image may become unclear, and furthermore, the stray light may affect the formed image significantly in the case of a color copy.
Further, the length of the guide rail must be increased with maintaining the accuracy of a copied image when the magnification changing range is widened. Accordingly, if a fragile guide rail is used, the carriage may jolt to the right and left on the horizontal plane. As a result, a long and thick guide rail of high strength is required, which causes weight of the device and manufacture cost to be raised.
Furthermore, since a base plate should be provided with the main body of the device in order to mount the carriage drive mechanism thereon, the size of the device is increased as a whole, efficiency for shipping of the device becomes low and the cost of the device is increased.
Recently, a copy machine capable of producing a colored copy has become known. In such a copy machine capable of producing a colored copy of an original, a plurality of filters: M (monochrome); B (blue); G (Green); and R (red) filters, are selectively inserted between the original and the image receiving plane in order to obtain the image data corresponding to respective colors.
In this case, since a lens brings the different colors of light of focus at different points, i.e., a chromatic abberation exists, it is necessary to use a lens having less chromatic abberation. However, the problem arises in that it is difficult to make a lens to have low chromatic abberation in various magnification ranges. Further, there exists a manufacturing error of the lens, and device, which makes it further difficult to compensate the chromatic abberation.